We are a commercial flat roofing company and regularly receive calls from people wanting to install or repair a residential flat roof. Our policy towards residential projects is we do not provide a free estimate. We are happy to look at a residential project and draft a proposal, but we do not do it for free.

If we provide a proposal and you decide to go with us, we deduct the cost of the estimate from the contract.

Similarly, residential roofing contractors receive calls and provide proposals to repair and install commercial flat roofs. This begs the question “Can a residential roofing contractor install and repair commercial flat roofs and, vice versa, can a commercial flat roofing contractor work on residential ones?”

The short answer is “yes”. But when you’re considering proposals, there are some differences between commercial and residential flat roofs that you need to be aware of. Taking these into consideration will help you make the best decision for you and avoid future unwanted problems and expenses. 

Similarities and Differences

The choice of roofing materials and basic design and installation methods used by commercial and residential flat roofing contractors is the same. There is no such thing, for example, as a roof membrane made specifically for commercial or residential use only.

When it comes to design and installation methods, both commercial and residential flat roof contractors should be using safe and effective methods to ensure the longevity and performance of the roof.

So what are the differences, if any? The main differences I have encountered come down to the pool of contractors that building owners have to choose from – how many of them are there, and is the quality of their workmanship the same?

How Many

If you own a 100,000 square foot commercial building, you should have the pick of the litter when it comes to contractors who want to install your new roofing system. The established contractors – the ones with a book of business and a solid track record – should all be clamoring to get your business. It’s a “buyers market” and building owners have the upper hand.

If, on the other hand, you own a 5,000 square foot residence, your pool of potential contractors is going to be different. For most commercial roofers, any project 5,000 square feet or less is considered a “small job”. If it is roofing season and established contractors are all very busy, they may decide to not even look at your property, never mind bid on the job. You, the homeowner, are going to be left with a much smaller pool of contractors to choose from, ones that likely do not regularly install flat roof membranes. That means the chance of your job suffering from one or more workmanship errors is greater.

Workmanship Quality

This is the biggest issue I see in the Southeastern Pennsylvania, Southern New Jersey, and Northeren Delaware market. Most roofs are not installed correctly or use substandard materials like a light-gauge edge metal more suitable for a shingle roof application.

If you live in a part of the country where most residential roofs are flat, you might have a good pool of contractors to pick from. It’s not the case in the Northeast United States, however, as most residential roofs are pitched and have shingles.

Design Considerations

As far as roof design is concerned, there are more aesthetic considerations on a residential flat roof than there are on a commercial one. For example, it’s acceptable to have a visible termination bar on a commercial flat roof. On a house, you should use edge metal at the perimeter and reglet (counterflashing) metal on any interior terminations.

If you are doing a single-ply membrane on a commercial flat roof, it’s probably better to do a fully adhered application vs. mechanical attachment because the roof will look tighter and have no wind movement. A house is more likely to have copper edge details vs. steel or aluminum on a commercial application.

Warranty Considerations

In the commercial space, the gold standard warranty covers labor and materials with a no dollar limit (NDL). This means if there is a leak that is covered under the terms of the warranty, the manufacturer will supply the materials AND the contractor’s labor cost to fix it. Additionally, there is a no dollar cap placed on the cost of the repairs.

In the residential space, the best I have seen is a material-only warranty. This means the manufacturer will supply materials to make repairs, but it is up to the homeowner to contract a roofer to affect them.

In Summary

So while many of the roofing materials and methods are the same when it comes to commercial and residential flat roofing, the pool of contractors you get to choose from can vary, and there are design and roof warranty differences that need to be taken into consideration.

My recommendation is to do your homework and choose your contracting company carefully. We have a list of questions you should consider asking to help you surface concerns you might need to be aware of before you make your final choice. We are, of course, available for consultation as well.